1. Field
This disclosure relates generally to semiconductors, and more specifically, to data processing systems that implement debug circuitry for monitoring information in the system.
2. Related Art
An IEEE standard known as IEEE ISTO5001, or the Nexus debug standard, is an established real-time debug standard that supports real-time debug message generation. The Nexus debug standard specifies a mechanism for identifying to an external trace reconstruction tool a predetermined operating condition within the system. Debugging processes are also used in the development of code for a data processing system. Providing debug information in real-time, without intrusion on the normal operation of the data processing system is highly desirable to remain transparent to operation of the system.
Debug messages are generated by the data processing system that contain address and data information for either program events (Program Trace Messaging), or data events (Data Read Messaging, Data Write Messaging), as well as other debug information. These messages help in the analysis and tracing of the progress of data processing in a system and are also referred to as debug trace messaging. The address information is typically virtual address information which is a format that must be translated to identify a physical memory location known as a physical address. Correlation of the address to a program undergoing execution is an important part of the debugging process so that actual program flow and the dynamic values of system data variables can be monitored. Virtual-to-physical address mapping or translation must be performed. However, an external debugger typically does not have the necessary virtual-to-physical mapping information to quickly translate the address portions of the debug messages, particularly when these mappings are dynamically changing due to demand paging or other remapping operations. The use of the virtual addresses allows a debug user a straightforward way to trace a computer program via a program listing obtained by a compile and link function which uses virtual addresses for text and data sections of the software application. The user typically has no knowledge of how the virtual addresses are translated to physical addresses by an operating system (OS). Therefore, tracing is required to indicate virtual addresses. Unfortunately certain program listings are unavailable, such as program listings for pre-compiled software modules which are executed at runtime. Examples of such modules are OS calls and library functions. In such an example, no program listing is available. Thus it is very difficult to properly trace and interpret these sections of the executed program. Correct translation of a virtual address to a physical address requires knowing where a program counter is and examining physical memory to determine where the address is. For systems executing multiple programs the memory mapping varies dynamically and readily transitions between memory pages. In such situations, the address translation significantly slows debug message generation and interpretation from being performed real-time.